For use in microwave integrated circuits (MIC) and monolithic microwave integrated circuits (MMIC), band pass filters such as the Ribbon-of-Brick-Wall (RBW) filter described in Coplanar Waveguide Bandpass Filter--A Ribbon-of-Brick-Wall Design, by Lin et al., IEEE, 1995, have been proposed.
The RBW coplanar waveguide (CPW) filter comprises a centerline surrounded by two ground planes in which a portion of the centerline is configured to have a quarter wavelength open ended stub conductor flanked by quarter wavelength open-ended stub resonators.
The RBW CPW filter of Lin et al. represents an improvement over prior art microstrip filters with respect to ease of series and shunt connections, absence of via holes, insensitivity to substrate thickness, and low dispersive effects. Notwithstanding these improvements however, the design of Lin et al. is disadvantageous in that it may permit propagation of spurious pass bands and DC bias voltages, and may suffer from moding which results in significant reductions in gain at frequencies corresponding to quarter wavelength multiples of the ground plane length.
In addition, conventional coplanar devices have expansive ground planes which take up a disadvantageously large amount of substrate area.